There are many more species of invertebrates (organisms that do not have a backbone) on Earth, than there are species of vertebrates. The Arctic is no exception to this rule. Expeditions to the Arctic have brought back samples of many coral and sponge species, some of which are enormous! Other common Arctic invertebrates include nudibranchs (sea slugs), sea stars, jellyfish, and crustaceans such as crabs and shrimp.